Below are various screenshots of this new code in action (it's live). The subscriber diagnostics and publisher diagnostics pages on the reference hub will let you see these stats for your feed or subscriber callback's domain (if you supply the right secret token). The redacted boxes protect sensitive URLs and stats.
Hub stats delivery to subscriber callbacks error rate (1 day window)
Hub stats delivery to subscriber callbacks latency (1 hour window)
Feed publisher statistics
Subscriber callback statistics